[llvm-pdbutil] Add an option to only dump specific module indices.

[llvm-pdbutil] Add an option to only dump specific module indices.

Often something interesting (like a symbol) is in a particular
module, and you don't want to dump symbols from all other 300
modules to see the one you want.  This adds a -modi option so that
we only dump the specified module.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310000 91177308-0d34-0410-b5e6-96231b3b80d8